This invention relates to a control valve, and more particularly to a control valve suitable for a construction equipment.
A conventional control valve of such type is generally constructed as shown in FIG. 1. More particularly, the control valve includes a valve body a formed therein with a neutral passage 1 and a first load check poppet 2 provided on a downstream side of the neutral passage 1. The first load check poppet 2 is adapted to permit fluid to be flowed only in a direction from the neutral passage 1 to a supply passage 3 communicating with an actuator (not shown).
The valve body a is also formed therein with a parallel passage 4 communicating with the supply passage 3 and provided therein with a change-over poppet 5 and a second load check poppet 6 between the parallel passage 4 and the supply passage 3.
The change-over poppet 5 is so arranged that its one end or distal end faces a pilot chamber 7, which is formed so as to communicate through a communication hole 8 and an annular groove 9 with the parallel passage 4. The other end of the change-over poppet 5 faces a spring chamber 11 having a spring 10 arranged therein. The spring chamber 11 is formed so as to communicate through an orifice 12 with the annular groove 9 and is connected through an on-off valve 13 to a tank 14.
In the conventional control valve constructed as described above, when pressure fluid is supplied through the neutral passage 1 to the valve body a, it opens the first load check poppet 2. This causes the fluid to be supplied to the feed passage 3 and then to the actuator (not shown).
When the on-off valve 13 is changed over from its closed position to its open position, fluid in the parallel passage 4 flows through the annular groove 9, orifice 12, spring chamber 11 and on-off valve 13 to the tank 14, so that pressure loss of fluid passed through the orifice 12 may occur across the orifice to generate on an upstream side of the orifice 12. The so-generated pressure is applied through the communication hole 8 to the pilot chamber 7, resulting in the change-over poppet 5 being moved against the spring 10 due to the pressure applied to the pilot chamber 7.
Such movement of the change-over poppet 5 causes the parallel passage 15 to communicate through the annular groove 9 with the communication passage 15. Therefore, pressure fluid flowing from the parallel passage 4 to the communication passage 15 opens the second load check poppet 6, resulting in being supplied to the supply passage 3.
Thus, the conventional control valve requires to provide the change-over poppet 5 and second load check poppet 6 separately. This leads to large-sizing of the control valve and complication of its structure.